Investigations on the Failure of In-Service 400-kV Composite Insulator

Composite insulators are gaining wider acceptance in distribution and transmission systems because of their promising characteristics. However, the long-term performance of the composite insulator is significantly affected by various electrical and environmental stresses leading to the degradation and aging of composite insulators. Recently, a new type of failure known as the decay-like fracture on fiber-reinforced plastic (FRP) rods has been reported in various countries. However, the progress and mechanism of this abnormal fracture are not entirely understood. In the present work, experimental studies, including Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray (EDAX), and thermogravimetric analysis (TGA), are conducted on the in-service fractured 400-kV composite insulator to investigate the structural changes in silicone housing and FRP rod, and the possible chemical reactions occurred. In addition, the performance of silicone housing and FRP rod is evaluated to study the effect of various stresses on the degradation and aging of the composite insulator by conducting equivalent salt deposit density (ESDD), nonsoluble deposit density (NSDD), wettability class (WC), hardness, tensile strength measurements, dye penetration, and water diffusion tests. The primary reason, mechanism, and development of this type of fracture are discussed. Also, a 3-D model of the fractured insulator is simulated using COMSOL multiphysics, and a preventive measure by optimizing the corona ring design is proposed and discussed.